Seeds and seedlings
Estimate the number of seeds you need
The number of seeds to start is not always the number of plants you want to keep. A useful estimate makes that difference visible. Begin with the final target, enter the rates you have reason to use, and keep the result labeled as an estimate rather than a promise.
Reviewed Oct 27, 2026
Start with the plants you intend to keep
Use the number of final plant positions as your target. You can get that count from a measured layout or enter it yourself. Do not count the same spare plants twice by adding them to the target and again as an extra reserve unless that is a deliberate decision.
For a purchased seedling plan, a seed estimate may not be the question you need to answer. Keep the target count useful on its own, and record whether you are starting seeds, buying seedlings, or combining the two.
Separate germination from later survival
Germination describes the share of the seed units you expect to germinate. Seedling survival describes the share of those germinated seedlings you expect to reach the target stage used by your plan. Enter the percentages you intend to assume; SowWindow does not know the condition of your seed lot or nursery.
A packet, supplier information, or your own test may help you choose an assumption, but the value should retain its context. Avoid treating a number from a different crop, seed lot, or growing setup as a universal default.
Read the worked estimate
For 40 target plants, 80% germination, 90% seedling survival, and no extra reserve, the combined assumed establishment rate is 0.8 × 0.9 = 0.72. Divide 40 by 0.72 to get about 55.56, then round upward once to obtain 56 seeds.
The upward rounding matters because a fraction of a seed is not a useful purchase or sowing instruction. It does not make the biological assumptions exact. If the real rates differ, the final number of plants can still differ from the target.
If you choose a 10% extra reserve with those same rates, the target allowance becomes 44 before dividing by 0.72, giving 62 after the final upward rounding. This makes the reserve’s effect visible rather than hiding it inside either percentage.
| Your input | Example |
|---|---|
| Target plants | 40 |
| Germination | 80% |
| Seedling survival | 90% |
| Extra reserve | 0% |
| Rounded estimate | 56 seeds |
Review the result before using it
An entered rate of zero cannot produce a finite seed estimate for a positive target. Correct the value rather than accepting a zero result or an infinite number. Rates above 100% are also invalid. The error belongs to the input assumption, not to the crop.
Check what one seed unit means for the material you are using. A simple estimate is easiest to interpret when one unit corresponds to one possible seedling. If your seed material has another structure or the supplier describes a different counting unit, keep that qualification with the estimate.
Save the assumptions with the number
Write down the target, percentages, and reserve setting beside the result. A bare number such as “56” is hard to reuse later. Recalculate when you change the layout or assumptions, and keep an editable backup if you want to compare the plan with what actually happened.